Many military records are at the Family History Library, the National Archives, and other federal and state archives. The United States Wiki article provides more information on the federal records. For California the following sources are especially helpful:

Fort McDowell -- Textual records of this fort, 1865-1890, including registers, reports, and correspondence, are in the National Archives and are described in Records of United States Army, Continental Commands, 1821-1920, under the section entitled Records of Posts, 1820-1940 (Record Group 393.7). The Fort McDowell Website describes the activity and history of Fort McDowell during the Spanish American War and subsequent years. Gives numbers of individuals processed during the different time periods, however it does not appear to give the names of those individuals.

Fort Moore -- was located in what is now downtown Los Angeles. It was built by the First Iowa Volunteers (Mormon Battalion) in 1847 and was abandoned as a U.S. military installation in 1849. See Church News for week ending July 19, 2008.

Civil War (1861-1865)

See California in the Civil War for information about California Civil War records, web sites, etc. with links to articles about the California regiments involved in the Civil War.

The regimental pages often include lists of the companies with links to the counties where the companies started. Men in the companies often lived in the counties where the companies were raised. Knowing a county can help when researching more about the soldiers and their families.

The Civil War Soldiers and Sailors System allows name searching for soldiers. The result set gives the regiments for the soldiers. Then you can check the Wiki regiment pages to determine counties. Often knowing the counties that had men in a regiment will help you determine if a soldier was your ancestor.

World War I (1917-1918)

World War I draft registration cards for men age 18 to 45 may list address, birth date, birthplace, race, nationality, citizenship, and next of kin. Not all registrants served in the war. For registration cards for California, see:

United States. Selective Service System. California. World War I Selective Service System Draft Registration Cards, 1917-1918. National Archives Microfilm Publications, M1509. Washington, D.C.: National Archives, 1987-1988. (Beginning on Family History Library film 1530652.)

To find an individual's draft card, it helps to know his name and residence at the time of registration. The cards are arranged alphabetically by county, within the county by draft board, and then alphabetically by surname within each draft board.

Most counties had only one board; large cities had several. A map showing the boundaries of individual draft boards is available for most large cities. Finding an ancestor's street address in a city directory will help you in using the draft board map. There is an alphabetical list of cities that are on the map. For a copy of this map see:

United States. Selective Service System. List of World War One Draft Board Maps. Washington, D.C.: National Archives. (FHL film 1498803.)

Additional Records

The California State Archives has military records from the California Adjutant General's office dating from 1849 to 1945. These include papers of the California Militia from 1850 to 1916, registers of California Volunteers in the Civil and Spanish-American Wars, records of California National Guard Units, and enlistment records from World War I and World War II. The Family History Library has microfilm copies of some of these records from 1858 to 1923 on 35 rolls. Records from World War I that include name, biographical, geographical, and newspaper card files are on the last 17 rolls of this set.